Vacuum cleaner



1955 K. J. WAHLBORG VACUUM CLEANER 6 Sheets-Sheet 1 Filed Feb. 19, 1955 INVENTOR. 422

ATTORNEY K. J. WAH LBORG VACUUM CLEANER Nov. 15, 1955 6 Sheets-Sheet 2 Filed Feb. 19, 1953 INVENTOR.

Nov. 15, 1955 K. J. WAHLBORG 2,723,724

VACUUM CLEANER Filed Feb. 19, 1953 6 Sheets-Sheet I5 14 A4006 L" I I I 1 I 0 0, 0,6 ,8 /,o /,2 4 y g Nov. 15, 1955 K. J. WAHLBORG 2,723,724

VACUUM CLEANER Filed Feb. 19, 1953 6 Sheets-Sheet 4 l l I F4 5757'! lb 80. 3a 5a. 6a

IN VE TOR.

arm/mm K. J. WAHLBORG VACUUM CLEANER Nov. 15, 1955 6 Sheets-Sheet 5 Filed Feb. 19, 1953 Nov. 15, 1955 K. J. WAHLBORG VACUUM CLEANER 6 Sheets-Sheet 6 Filed Feb. 19, 1953 \w QR AR INVENTOR. BY $74. $14

{ad/f A ATTdfi/VZF) VACUUM CLEANER Karl John Wahlborg, Bromma,

bolaget Elektrolux, of Sweden Sweden, assignor to Aktie- Stockholm, Sweden, a corporation This invention relates .to vacuum cleaners, and more particularly to horizontal tank type cleaners provided with centrifugal fans which develop a relatively high vacuum while moving relatively small quantities of air. This application is a continuation-in-part of my application Serial No. 58,215, filed November 4, 1948, now abandoned.

In vacuum cleanersof this type removal of dust and dirt from objects to be cleaned is efiected by flow of air which is produced by motor-driven centrifugal fans, and no mechanical working of the objects takes place which is true of other types of vacuum cleaners making use of revolving brushes, for example. A horizontal tank type vacuum cleaner includes an elongated outer shell or casing within which are retained a dust bag for collecting dust and dirt, a centrifugal fan unit'and an electric motor for driving such fan unit. During operation of the vacuum cleaner, air is drawn into one end of the casing by the'suction developed by the centrifugal {an unit The dust bag is located at the air inlet end of the casing, and air and dust entrained in the air during'a cleaning operation are separated from, the air when the latter passes through the dust bag Air free of dust and dirt passes through the dust bag and flows through the casing and is discharged from the opposite outlet end thereof, such path of flow of air free of dust and dirt being through that portion of the casing in'which the centrifugal fan unit andelectric motor are positioned.

While a vacuum cleaner is employed for suction cleaning of many different objects, one of its most important uses is that of cleaning carpets and floors; In such case a nozzle is manipulated over the surface to be cleaned with a wand or tube, the nozzle being attached to one end of the tube while the other end thereof is connected by a flexible hose to.the suction inlet'end of the easing. When the nozzle opening is fully closed and the flow of air through the casing is stopped, the vacuum produced by the cleaner is at a maximum; When the inlet of the nozzle is completely open, which usually is referred to as full opening, the rate of air flow through the casing is at a maximum and the vacuum produced is at a minimum. In this way data can be obtained in which the suction developed at different nozzle openings can be tabulated for a so-called suction test."

The rate at which electrical energy is consumed by the electric motor during operation of the vacuum cleaner represents the power input required to operate the appliance. Only a fraction of this power input is utilized as useful power for vacuum cleaning purposes because of losses which occur in the motor, dust bag, hose and other parts defining the path of air flow. Such power loss is converted into heat which results in heating of the vacuum cleaner and also the air discharged therefrom. The power remaining for useful vacuum cleaner work is that with which the air flow is charged when entering the inlet of the nozzle and is a product of the vacuum produced (kg/m9, for example) and air 2,723,724 Patented Nov. 15, 1955 "ice volume (m. /second, for example). Such power available for useful vacuum cleaning purposes may be referred to as suction power. By computing the ratio of the suction power to the power input to the vacuum cleaner, the efficiency (1 of the vacuum cleaner can readily be determined.

The ability of a horizontal tank type cleaner to remove dust and dirt may be referred to as its dust absorption capacity. -One factor which influences dust absorption is the speed of the air flow through the nozzle, wand and hose for bodily moving and transporting dust and dirt particles from the object to be cleaned to the dust bag. In a moving air stream, movement is imparted to a particle of dust or dirt by a force which is dependent upon positive atmospheric pressure at one side of the particle and a pressure at the opposite side thereof which is below atmospheric pressure. The speed of the air flow increases with increase in the volume of air moved, and increasingly heavier particles can be drawn into the air flow with such increase in the volume of air moved. In this instance the vacuum developed by the cleaner does not affect the bodily movement of the dust and dirt particles as long as the air flow path is not completely clogged, which is true, for example, when a ball of paper becomes caught in the hose. When such clogging occurs, a situation arises where movement isimparted pneumatically to matter caught in the path of air flow by a force which is dependent upon the diiference between atmospheric pressure and the vacuum developed by the cleaner.

, In cleaning carpets and fabrics and similar porous objects where dust and dirt must be sucked or drawn from the pores of an object, the pneumatic force just referred to as well as the speed of the air are factors which necessarily are present during a cleaning operation to effect loosening of dust from the porous object. However, investigations show that the dust absorption capacity of a vacuum cleaner on the whole is proportional to the product of vacuum and air volume and hence proportional to what has been referred to above as suction power. While other factors are present when the problem of dust absorption is considered in its entirety, such as, for example, the capacity of brushes and nozzles working mechanicaly on objects, it is nevertheless a primary and basic consideration that in all instances the ability of a vacuum cleaner to suck and absorb dust will be increased when the vacuum, air volume and suction power of the cleaner are increased.

In recent years there has been a tendency to employ motors of larger capacity and higher speed for driving centrifugal fans units at a higher speed to increase the dust absorption capacity of vacuum cleaners. While a motor of larger size will increase the cleaning ability of a vacuum cleaner, this is done at the expense of higher operating cost by reason of the additional electrical energy required to operate the motor of higher power rating. Further, there is a tendency toward increase in motor Weight with. the use of motors of higher power rating, thereby tending to increase the overall Weight of the vacuum cleaner. Also, the diameter of the centrifugal fan unit may be increased to improve the cleaning ability of vacuum cleaners. In such case, an outer shell or cas ing of larger size will be required. The methods just described forimproving the cleaning ability of vacuum cleaners are objectionable because there is a tendency for the vacuum cleaner to be proportionately heavier and larger in size and hence less convenient to use during cleaning operations.

It is an object of my invention to provide an improved horizontal tank type vacuum cleaner in which the dust absorption capacity is markedly increased without the necessity of increasing the overall size or weight of the vacuum cleaner and without any increase in operating cost. I accomplish this by providing a centirfugal fan unit capable of developing optimum suction power in a horizontal tank type vacuum cleaner of a given crosssectional area.

It is another object of the invention to provide an improved horizontal tank type vacuum cleaner having such a centrifugal fan unit whereby the suction capacity of cleaners of this type is increased without any essential increase in the speed at which the fan units are driven, thereby avoiding any increase in friction or power losses.

A further object of the invention is to provide an improved horizontal tank type cleaner having such a centrifugal fan unit which will enable the cleaner to operate at or substantially at the optimum efficiency when absorbing dust from porous objects like carpets, for example, such optimum efiicency being advantageously realized during a cleaning operation where the cleaner nozzle must be pressed against the porous object to create substantial resistance to air flow and cause a comparatively small air flow through the cleaner.

The improved efficiency and performance of horizontal tank type vacuum cleaners provided with centrifugal fan units embodying the invention is dependent upon the existence of a particular relationship between the various diameter measurements of the fan wheel, fan screen and fan housing, This relationship provides a centrifugal fan unit in which the air passages through the unit effect a throttling action to flow of air therethrough and exists when the diameter of the fan screen is greater than that of the fan wheel and the ratio of the product of the diameter of the fan housing and outer diameter of the fan screen to the product of the fan housing inlet and fan wheel inlet is in a range between 11 and 19. While the improved suction effect or higher vacuum developed by fans of the invention can be obtained without any increase in size of the fan housings, it has been found that an increase in the size of the fan housing within certain limits further increases the suction effect or vacuum developed.

In the specific embodiments disclosed herein which are illustrative of the invention, fan units having a definite relationship between the several fan parts are incorporated in fan units in which the fan screen is transverse to the axis about which the fan wheel rotates and is formed with a free outer peripheral edge, and the housing includes a wall part extending axially of the unit past the outer free edge of the screen to form an air gap therebetween for flow of air therethrough from the outlet of the fan wheel.

The novel features which are believed to be charactris: tic of the invention are set forth with particularity in the claims. The invention itself, however, both as to organ; ization and method, together with further objects and ad.- vantages thereof, will be better understood by reference to the following description taken in connection with the accompanying drawings in which:

Fig. 1 is a sectional view diagrammatically illustrating a fan system of known type intended for use in a horie zontal tank type vacuum cleaner; V

Fig. 2 is a sectional view similar to Fig. l diagrammatically illustrating a fan system for horizontal tank type vacuum cleaners which embody the invention;

Fig. 3 is a sectional view similar to Fig. 2 diagram-v matically illustrating another form of fan system for vac.- uum cleaners which embodies the invention; I

Fig. 4 is a sectional view of a fan system of a type compared with the fan systems of Figs. 1, 2 and 3;

Figs. 5 to 8 are curves diagrammatically illustrating the performance characteristics of fan systems embodying the invention and other fan systems for purposes of comparison, and also the perforance characteristics of vacuum cleaners in which such fan systems are incorporated; l H

Fig. 9 is a curve showing the effect of various changes characterizing the development of fan systems like those shown in Figs. 2, 3 and 4; and

Figs. 10 and 11 are side views, partly in section, of horizontal tank type vacuum cleaners illustrating preferred arrangements for embodying fan systems of the invention in the outer shell or casing of such cleaners.

In Fig. 1 is diagrammatically illustrated a two-stage centrifugal fan system of a type which has been used in horizontal tank type vacuum cleaners, and like that disclosed in United States Letters Patent No. 2,242,333 of S. F. Thunberg, granted May 20, 1951. Such a fan system includes rotary fans or fan wheels 10 and 11 fixed to a shaft 16 adapted to be driven by a suitable electric motor M, only a fragmentary portion of which is shown. The tandem fans 10 and 11 are disposed within housings 14 and 15, respectively, which form suction creating fan chambers. The fan system and motor M are disposed in adjacent axially extending sections of the interior of the vacuum cleaner housing.

The housings 14 and 15 include Walls 17 and 18, respectively, which are normal or perpendicular to the shaft 16, Rotating movement imparted to the shaft 16 causes the fans 10 and 11 to draw air through an inlet opening in the wall 17 into the housing 14, and from the latter air is drawn through an inlet opening in the wall 18 into the housing 15. Fan screens 12 and 13 are fixed in position alongside the fans 10 and 11, respectively, at the sides thereof opposite the inlet openings formed in the walls 17 and 18.

In Fig. l dh indicates the diameters of the inlet openings of the suction creating chambers, and Dn indicates the diameters of such chambers which are also referred to as fan housings. D5 indicates the diameters of the fan screens, and Dw indicates the diameters of the fans 10 and 11, that is, the outer diameters of the fan wheels. Air drawn through the inlet openings in the walls 17 and 18 passes through cooperating inlet openings in the fans 10 and 11 which are indicated as d and such air is discharged radially outward by the fans.

A primary characteristic of fan systems intended for use in horizontal tank type vacuum cleaners, and like that shown in Fig. 1 and just described, is that such a system must be capable of producing a high vacuum with comparatively small quantities of air. For this reason fan wheels of the centrifugal type are employed which are driven at relatively high speeds. In order to increase the vacuum or suction effect that can be produced by a vacuum cleaner, there has been a tendency to use electric m r of h h r ati t nc e e he p e at which. such fan wheels are driven. However, increasing the speed at which fan wheels are driven increases the power losses resulting from increased friction losses at the outer sides or end surfaces of the fan Wheels. Such power 93.5 Pr ma e xpr d by e qu in which C is a'constant, n is the speed in R. P. M. and D is the outer diameter of the fan wheel. Hence, the power losses of centrifugal fans is a primary factor when consideration is given to increasing fan speeds, and there has been a tendency to reduce the outer diameters of centrifugal fans in order to avoid excessive friction losses when the speeds at which they are driven are increased. When fans having a smaller outer diameter are employed, it is then necessary to increase further the speed at which such fans are driven to obtain the desired higher vacuum. The foregoing analysis characterizes the trend of development of vacuum cleaner fans because over a period of time there has been a change from fans of larger diameter to fans of smaller diameter, and with such change the speed at which the fans are driven has been increased.

In accordance with this invention, the suction capacity of a horizontal tank type vacuum cleaner provided with a fan system like that shown in Fig. l and just described, in. which the shaft 16 is horizontally disposed, was improved considerably by replacingsuch fan system bythe fan system diagrammatically illustrated in Fig. 2. Such improved suction effect or higher vacuum is obtained in Fig. 2 without any need of increasing the speed atwhich the fans are driven by the motor M, thereby avoiding any increase in friction or power losses. When Fig. 2 is compared with Fig. 1, it will also be seen that such improved suction effect or higher vacuum is obtained without any increase in size of the fan housings. The parts of the fan system in Fig. 2 similar to the parts in Fig. 1 are designated by the same reference numerals with 100 added thereto.

The advantages of the invention can also be realized in vacuum cleaners in which the shaft to which thefans are fixed is disposed in a vertical position.v Such a fan system embodying the invention is diagrammatically shown in Fig. 3 for a vacuum cleaner of a larger size than'that for which the fan system in Fig. 2 is intended to be used, and replaces a fan system of known type like that shown in Fig. 1. The parts of the fan system in'Fig. 3 similar to the parts in Fig. 1 are designated by the same reference numerals with 200 added thereto. Y

The degree of efliciency of centrifugal 'fans can be expressed by the formula in which 1; (eta) is the degree of efiiciency, q is the quantity of air drawn into a fan per unit interval of time, H is the vacuum or suction elfect produced and P is the power or energy required to drive the fan. Such degree of efliciency for centrifugal fans capable of producing high vacuum generally increases with an increase in the ratio of the outer diameter of the fan to the diameter of the fan inlet opening, that is, the diameter'ratio Dw/dw. When the outer diameter of a fan is decreased, the diameter dw of its inlet opening desirablyshould also be reduced in order to maintain a desired degree of efficiency for the fan. However, it has been found that when the diameter dw of the inlet opening is decreased for a given fan wheel whose outer diameter is Dw, a limit is finally reached in the size of the inlet opening at which, in connection with the greater quantities of air being moved, the degree of efliciency no longer increases but instead decreases.

In Figs. 1, 2 and 3 it will be seen that all of the fans illustrated have the same outer dimensions, that is, the same widths and outer diameters Dw. In other respects these fans are similarly developed with the exception that the diameters dw of the inlet openings are smaller for the fans 110 and 111 in Fig. 2 and the fans 210 and 211 in Fig. 3, which are in accord with the invention, than for the fans and 11 in Fig. 1 which are of a type that have been used in the vacuum cleaner art. Further, the inlet diameters db for the fan housings 114 and 115 in Fig. 2 and fan housings 214 and 215 in Fig. 3, and also the radial distances between the peripheries of the fan screens 112, 113, 212 and 213 and the housings 114, 115, 214 and 215, respectively, in Figs. 2 and 3, are less than the corresponding inlet diameters dh for the known fan housings 14 and in Fig. 2 and less than the corresponding radial distances between the peripheries of the fan screens 12 and 13 and housings 14 and 15, respectively, in Fig. 1. It will also be seen that the radial distances between the fans 10, 11, 110 and 111 and housings 14, 15,114 and 115, respectively, in Figs. 1 and 2 are the same while the radial distances between the fans 210 and 211 and housings 214 and 215, respectively, in Fig. 3 are greater than the corresponding radial distances in Figs. 1 and 2.

In the following description the embodiment in Fig. 1 will he referred to as fan system 1b, the embodiment in Fig. 2 will be referred to as fan system 2a," andthe embodiment in Fig. 3 will be referred to as fan system 34. The numerals in the designations indicate fan sys-' tems having difierent ratios between the several parts,

t 6 while the letter a indicates a fan housing and fan wheel havingsmall inlet openings and the letter b indicates a fan housing and fan wheel having larger inlet openings. For the three fan systems or embodiments of Figs; 1, 2

In the above data it will be understood that each of fans 10, 110 and 210 in Figs. 1, 2 and 3 is referred to as a front fan, while each of fans 11, 111 and 211 is referred to as a rear fan. This is so because air drawn into the fan housings is acted upon initially bythe fans 10, 110 and 210 in the embodiments of Figs. 1, 2 and 3.

:In order to bring out more clearly how the changes in the different ratios tabulated above influence the effi ciency of a fan system and also the shape of a curve representing suction efiect or vacuum performance, the "fan system 2a and fan system 3a of Figs. 2 and 3 have been compared with a fan system like that diagrammatically illustrated in Fig. 4 in which parts similar to those in Fig. 1 are designated by the same-reference numerals with 300 added thereto.- The embodiment of Fig. 4, which will be referred to as fan system 4a,"= is like the fan system in Fig. 2 in that the diameters of the inlets of the fan housings and fan wheels in FlgSJFZ and 4 are the same. Also, the outerdiameters Dw of the' fan wheels and diameters Dh of thefan hous-' ings in Figs. 1, 2 and 4 are the same. However, the diameters D3 of both screens 312 and 313 in'Fig. 4 are the same as the outer diameters Dw of the fan wheels 310 and 311, thus giving -a Ds/Dw ratio of 1.00 for both the front and rear fans. Hence, in Fig. 4 the Ds/Dw ratio for both fans is identical to that for thefront fan 10 in the fan'system 1b of Fig. 1.

Further, fan system 2a and fan system 3a of Figs. 2 and 3, respectively, which embody the invention, were compared with three additional fan systems deviating from the invention which will be referred to as fan system 2b, fan system 31;, and fan system 4b, thedata for which, together with that of fan system 4a, are tabulated below:

Fan Systern 4a 4b 2b 3b g (for both tans) 2. ss 2. 4o 2. 40 2. 40

D n (for both ians)... 3.65 2. 81 2. 81 3.13

DI (for front tan) 1.00 1.00 1.10 1.24

I (for rear tan) 1. 00 1. 00 1. 10 1. 22

From the above data it will be seen that the fan systems 2b, 3b and 4b differ from the fan systems 2a, 3a, and 4a in that the ratio Dw/dw for both fans is 2.40 instead of 2.88, and hence the ratio Dw/dw for both fans in the fan systems 2b, 3b and 4b is the same as that for the known fan system 1b. Further, the fan systems 2b and 4b differ from the fan systems 2a and 4a, respectively, in that the ratio Dh/dh for both fans is 2.81 instead of 3.65. The fan system 3b differs from 7 the fan system 3a in that the ratio Dh/dh. i! both fans is 3.13 instead of 4,05. I When the data tabnlatedfor fan system 4b is compared with that for fan system 1b which is of the known type, everything is the same except the ratio Ds/Dw for the rear fan. In fan system 1b the ratio Ds/Dw for the rear fan is 1.08 and the average for both fans is 1.04, whereas in the fan system 4b this ratio is 1.00. Hence, the fan system 4b is obtained when the diameter D of screen 13 in Fig. 1 equals the diameter D of the rear fan wheel 11. Nevertheless, the fan system 4b has been selected in order to bring out as clearly as possible the advantages realized from the fan systems 2a and 3a in which the several parts have a particular relationship.

The six fan systems 2a, 3a, 4a, 2b, 3b and 4b were tested in a motor fan unit, the same electric motor being employed in testing each fan system. The motor fan unit was attached to an equalization vessel provided with an aerometer and outlet to measure the vacuum. For each of the six fan systems, suflicient test data were taken to plot curves illustrating performance characteristics. The test data obtained for the purpose of com? paring the performance characteristics of the different fan systems were taken at essentially the same maximum electrical power inputs (watt-s) to the motor while supplying electrical energy thereto at the same operating voltage. In this way the test data taken for all of the fan, systems indicated changes in performance characteristics directly attributable only to differences between the several fan systems.

-In Fig. 5 are shown curves illustrating the performance characteristics plotted from test data which were obtained with the aid of the motor fan unit just referred to for fan sysems 2a, 3a, 4a and 4b. In Fig. 5 the volume of air q drawn into a fan system per unit interval of time is indicated along the abscissa while the suction effect or vacuum H, the electrical power consumption P. and speed ,n are indicated along the vertical ordinate.

Each curve is appropriately identified to. indicate. the par-- ticular fan system whose performance characteristic is illustrated. For example, the curves identified as m Hz, and P29. illustrate the performance characteristics for the fan system 2a, namely, the variations in speed- (R. P. M.), vacuum and power consumption with changes in the volume of air drawn into the fan system per unit interval of time. In a similar manner the other n, H and P curves indicate the performance characteristics for the fan systems 341, 4a and 4b.

Fig. 5 also includes curves h and hz obtained from plotting changes in the total air resistance developed in I two different types of vacuum cleaner structures against changes in the volume of air moved through such struc: tures per unit interval of time. By total air resistance is meant the resistance developed in the hose and the tubular handle, bag, filter and structural parts of each vacuum cleaner structure. The resistance curve he illustrates the resistance characteristics of the vacuum cleaner of horizontal type referred to above in connection with the description of the fan systems 1b and 2a shown in Figs. 1 and 2, respectively.

With the aid of the resistance curves hi and Hz, the curves in Fig. 5 illustrating the performance characteristics for the fan systems can be translated or reduced to curves representing the performance characteristics for complete vacuum cleaners of both types identified by these resistance curves. By translating and reducing the performance characteristic curves in Fig. 5 by rneans of resistance curve in, it is possible to obtain the curves illustrated in Fig. 6 which represent the efficiency 1; and vacuum I-I curves for the horizontal type vacuum cleaner adapted for operation with the fan systems 11 2a, 3 a and 4b, respectively. Also included Fig. 6, is a curve His rcpresehting the vacuum characteristics for the hori: zontal type vacuum cleaner provided with fan system 11;. The curve Hrs was obtained from test data with a certain maximum electrical power input to the fan motor resulting in a vacuum curve which coincides quite closely with the vacuum curve H4.

It has previously been stated that Figs. 2 and 3 illustrate fan systems embodying the invention which are referred to as fan systems 2a and 3a, respectively. On the other hand, the embodiment shown in Fig. 4, referred to as fan system 461, and also the fan system 4b, deviate from the embodiments of Figs. 2 and 3. It appears from the curves in Fig. 5 for the fan systems, 4a, 2a and 3a that the gain resulting from the throttling of the passages at the regions between the fan screens and the fan housings and effected by increasing the outer diameter D5 of the fan screens in these embodiments from the known embodiment in Fig. 1 (fan system 1b), and the gain effected in the fan system 3:: resulting from the increase in the radial distance between the fan wheel and fan housing and effected by increasing the diameter Dr; of the fan housing, is obtained although the diameters a' and dn of the fan wheel inlets and fan housing inlets, respectively, are the same in all three fan systems or embodiments 2a (Fig. 2), 3a (Fig. 3) and 4a (Fig. 4).

In Fig. 8 are shown curves representing the performance characteristics for the fan systems 2b, 3b and 4b. These curves are similar to the performance curves in Fig. 5, and, in order to show the difference between the curves in Figs. 5 and 8, the performance curves for the fan system 4b are illustrated in both figures. The performance curves for the fan systems 411, 2b and 3b show the result of the same increase of the diameter D; of the fan screen as for the fan systems 4a, 2a and 3a, and the same increase of. the diameter Dh of the fan housing as for the fan system 3a. However, the performance curves for the fan systems 4b, 2b and 3b differ from those for the fan systems 201 and 3a inasmuch as in the former the throttling of the fan wheel inlets and fan housing inlets (11v; and db), respectively, has not been effected as in the latter according to the invention.

When the vacuum performance curves H in Figs. 5 and 8 are observed, it will be seen that the improved performance of embodiments 2a and 3a over the performance of embodiment 4a is much greater than the gain in vacuum performance of embodiments 2b and 3b over the performance of 4b. This result is obtained although the diameters D5 of the fan screens for the embodiments 2a and 2b are increased the same amount and in the neighborhood of about 10%, and although the diameters D5 and Dh of the fan screens and fan housings, respectively, for the embodiments 3a and 3b are increased the same amount and in the average of about 23%. Hence, the improved vacuum performance is proportionately greater for the fan systems 2:: and 3a which have a higher diameter ratio Dw/dw of 2.88 between the outer and inlet diameters of the fan wheel that throttles the inlet than for the fan systems 2b and 3b which have a smaller diameter ratio Dw/dw of 2.40.

' The performance characteristics of a fan wheel are closely connected and interdependent with changes in the diameter ratios Dav/div and Dh/dh of the fan wheel and fan housing, respectively, and with changes in the diameter D5 of the fan screen. in other words, such changes exercise considerable effect on the ratios between vacuum, quantity of air moved, speed and power consumption. The result of the various changes characterizing the development from the known fan system, which is representedby the fan system 4b since it closely approximates the fan system 1b, to. the fan systems 2:: and 3a according to the invention, is clearly evident in Figs/5 and 6, especially the efiiciency (1 curves for the fan systems 1b, 4b, 211 and 3a in Fig. 6.

As previously stated, Fig 6 illustrates curves repre-. senting the performance characteristics for a complete vacuum cleaner structure. In practical use such vacuum cleaner is adapted to move a variable quantity of air :1 per unit interval of time in a range represented along the abscissa in Fig. 6 from the intersection thereof with the ordinate to the region of the reference character q. Within the entire operating range'it will be seen that the vacuum performance curves H311 and H23. for embodiments 3a and 2a are higher than the vacuum performance curve for the embodiment 4b. The suction capacity of the vacuum cleaner, that is, the product of the suction eflfector vacuum and quantity of air moved, at any point within the entire operating range and primarily Within the mean operating range, will therefore be higher when adapted to be operated by the fan systems 3a and 2a than by the fan system 4b.

When reference is made to Fig. 5, it will be'seen that the power consumption curves P21, P33. and P4bf01' the fan systems 211, 3a and 4b are practically identical. The increased suction capacity shown by the fan systems embodyingthe invention, that is, fan systems 3a and 2a, is

thus'due to higher degree of efliciency of these fan systems compared with that of the known fan system. This isapparent in Fig. 6 which shows the efliciency curves 1; of vacuum cleaners adapted for operation with these fan systems.

In Fig. 5 it will be observed that the speed n (R. P. M.) to obtain the higher suction effect or vacuum for the fan systems 3a and 2a-is represented by the curves na and 7122, while the speed for the known fan system is represented by .the curve "4b. The diiference in the speed characteristics of these fan systems is comparatively small, so that the increase in speed to obtain the higher suction effect for the fan systems of the invention is not great. The speed curves mi) and 713a practically'coincide. while the speed curve I129. is located relatively low. .Hence, the increase in suction effect or vacuum obtained by the embodiments 3a and 2a is etfected without essential increase in speed. This means that the degree of reaction, that is, the proportion or ratio at which the work performed on the air by the fan blades is converted into pressure energy, is greater for fan systems of the invention than for the known fan system.

Hence, in fan systems of theinvention, a higher-suction capacity is obtained over the entire operating range of the vacuum cleaner, and this is effected with comparatively low electrical energy consumption and at relatively low speed. For example, the value of suction effect or vacuum when the quantity of air moved by a'fan system is zero is referred to as zero vacuum. When the zero vacuum of the known fan system is increased to a value corresponding to that obtained by fan systems of the invention, it is necessary to increase the speed of the known fan system by about 10% and the electrical energy consumption (watts) by about 25%; However, in fan systems of the invention, such increase of zero vacuum has been obtained without any essential increase, in electrical energy consumption and speed, the increase in zero vacf uuin instead being due to the improvement in the degree of efiicien'cy and degree of reaction, as explained above.

Figs. 5 and 6 also show that the vacuum performance curves Him. for the fan system 3a is more rounded-out and more convex in shape than the vacuum curves Hz; for the fan system 2a. Hence, it is advantageous to increase the diameter Dn of the fan housing and diameter D5 of the fan screen for a given fan wheel diameter D... As will appear from the drawing, in the two embodiments according to the invention. the radial distance Dh-Dw In other words, the upper limit for D5 is met when it is equal to or less than D D D, 17 16; can be calculated for each fan system. When this is done for the fan system described above, the following results are obtained:

Fans according to the invention:

Product Value Fan system 2a, both fans 11. 6

Fan system 39., front tan 14.5

Fan system 32., rear tan 14. 2

Known fans:

Fan system 1b, front fan 6. 7

Fan system 1b, rear fan; 7. 3

Fans constructed for comparative tests:

Fan system 49., both fans 10. 5

Fan system 2b, both fans. 7. 4

Fan system 31), front fan 9. 3

Fan system 3b, rear ian.- 9. 1

Fan system 4b, both fans 6. 7

The above'tabulated results show that the product value" is higher for those fan-systems whose degree of re action or efiiciency,v respectively, is greater. If the diameters Dh and D5 for both fans in fan system 3a were increased further, the fan system would be improved in that the product value would also increase, but such improvement is proportionately smaller than the improvement efiected when changing from fan system 2a to fan system 3a. In changing from fan system 2a to fan system 3a, the increase infan housing diameter Dh over and beyond the fan housing diameter for fan system 4b amounts to 13% of the fan wheel diameter. In order to illustrate the improvementetfected with further increase in D21 and D5, vacuum and efiiciency performance curves are shown in Fig. 7 for two fan systems 5a and 6a as well'as for fan system 3a of the invention and the known fan system 4b. The fan wheels and fan housing inlets in the fan systems 5a and 6a are the same as in the fan system 30. However, the diameters of the fan housings and fan screens for the fan systems 5a and 6a are greater than for the fan system 3a, these dimensions being greater for fan system 6a than for fan system 5a. The diflerence in diameters of the fan housings for fan systems 3a and Sais about 9%, and the difierence in diam-- etersof the fan housings for fan systems 5a and 6a is also about 9%; ,The fan screen diameter is the largest for the fan system 6a in which instance it is about 40% larger than the outer diameter of the fan wheel.

Despite the fact that the increase in diameter of the fan housing between the fan systems 6a and 5a is the same as that between fan systems 5a and 3a, it is apparent from the curves shown in Fig. 7 that the improveme gained in ch n o .f ys em 5 o f n y m 6a s s ght nseq ly, a l mit an b es a li he yo d hi h i s n or hwh le to effe a furthe increase in the diameter of the fan housing which in turn determines the size in cross-section of the vacuum cleaner c g- To faci ate n und rstan ing of h manner in hi h s h limi can be esta lish d, h following ata is tabulated for the fan systems 511 and 6a.

Fan System 5a 6a D I (for both tans). 2.88 2.88

Dh I i i l (for both fans) 4. 32 4. 59

D. (for the front fan).... 1.32 l. 42 D W D- (for the rear fan) 1. 30 1. 40 D VI The product of the expression a esa din b .Dw for the fan systems 5a and 6a are indicated below:

Product Value Fan system 5a, front tan 16. 4

Fan system 59., rear fan 16.2

Fan system 621, front tan 18. 7

Fan system Gin rear tan.. I 1 85 By means of the product values determined from the expression Dw h E i w h s v d.',, d,, can therefore be written I d;, d..,' and the expression for fans constructed according to the invention is D hX a h w Therefore, in a fan constructed according to the invention, the fan wheel, fan housing and fan screen have such a relationship that the ratio of the product of the diameter of the fan housing and outer diameter of the fan s r t he product of the, iam er f th ,fa h u ing nlet and f n whee inl is eq a t or g ater h n bu smaller than or equal to 19. This ratio between and inlit val n. su h a f n cons ruc ed according to he iuveu: ou. e un sc een is dispo l gsi th f n wheel at the side thereof opposite the fan inlet, the diameter of the fan screen being greater than the outer diameter of the fan wheel.

In view of the foregoing, it will now be understood that I have discovered that the above-defined product value, namely, a specific relationship between the throttling effect at the fan wheel outlet and the rate at which air is drawn into the fan housing and fan wheel inlets, is of critical importance. Fig. 9 shows a curve obtained are perimentally to determine the product value necessary to obtain the technological improvement in accord with the invention, that is, the highest increase in efiiciency over the known fan system 1b correlated to the product values calculated by the expression given above. Stated an other way, the product values characterizing different fan systems are indicated along the abscissa, and the gain or increase in efficiency is indicated along the ordinate for different fan systems in which the outer diameter of the fan wheel remains the same. Hence, the curve of Fig. 9 essentially shows the changes in efiiciency with changes in the outer diameter of the fan housing (D11) and outer diameter of the fan screen (D5), for example, as previously described above in explaining the reason for including the curves for fan systems 5a and 6a.

In order to obtain the curve shown in Fig. 9 the maximum efficiency values for different fan systems were obtained from curves like those shown in Figs. 6 and 7, and the product values for such maximum efficiency values noted. In the table below such values are tabulated, the product value indicated being the average when different values are given above for the front and rear fans.

Fan Maximum 1 Product A" Maxirfmm= A17 System (efficiency) Value Ii 1b 19. 6 7. 0 0 0 3a 23. 2 14. as i 3.6 Y .251

The above table also includes data for an additional fan system having a fan wheel with the same outer diameter as the other fan systems and a product value of 26.2. In addition to tabulating the maximum efficiency (1;) for a given fan system and the product value therefor, the above data in the next to last column indicates the increment of increase in efficiency (An) of the last four fan systems 2a, 3a, 5a and 6a over the known fan system 1b. In the last column the increment of increase in efficiency is related to the product value for each fan systern in order to obtain a true representation of the character of changes necessary, such as an increase in D11 and D5, as explained above, for the resultant technological improvement effected. In Fig. 9 the product values for the different fan systems are indicated along the abscissa, and the gain in efficiency An max. Product value is indicated along the ordinate. The maximum gain in efficiency occurs when the product value is substantially 15. A larger or smaller product value indicates a reduced increase in efiiciency. For example, the maximum gain in efficiency is about 28 per cent for the product value of 15 while the gain in efliciency for product values of 11 and 19 are about 17.5 and 26 per cent, repectively. A product value of substantially 15 and'not less than 11 cluding 11 and 19 may be referred to as the product nor more than 19 is preferred, the limits in the preferred 13 range of product values being larger and smaller than 15 by about the same amount.

In the embodiments of the invention described above, it will be seen that the fan housing includes a wall part extending axially of the fan unit past the outer free edge of the fan screen to form an air gap therebetween. Hence, air discharged radially outward from the outlet of the fan wheel then flows axially of the unit through such air gap to a region defined in part by the rear side of the fan screen, that is, the side thereof facing the direction of air movement. This enables air in its path to flow through the fan housing to pass over the vicinity of the rear side of the fan screen.

In Fig. I have shown a horizontal tank type vacuum cleaner provided with a fan system of the invention and of the kind illustrated in Figs. 2 and 3 and described above. The vacuum cleaner of Fig. 10 comprises an elongated outer casing 20, a removably connected front end cover 21 having a central opening 22 to which is adapted to be connected a flexible suction tube or hose (not shown), and a removably connected rear end or cap 23 having a transverse end wall 24 formed with a number of apertures 25 distributed about the periphery thereof, such apertures defining the exhaust or discharge opening for air passing from the cleaner. An apertured end plate 26 is secured at 27 to the end wall 24, these parts being adapted to retain a filter pad therebetween (not shown) through which discharged air passes.

Within the casing 20 is provided a perforated partition or wall 28 at one side of which is disposed a dust bag 29 for collecting dust and dirt. At the opposite side of the partition 28 is disposed a fan motor unit including rotatable fan wheels 110a and 111a fixed to a shaft 116a adapted to be driven by an electric motor 30. The tandem fans 110a and 111a are disposed within'a fan housing 31 having suction creating chambers 114a and 115a formed with inlets in the transverse walls 117a and 118a, respectively. Fan screens 112a and 113a are fixed in position alongside thefans 110a and 111a, respectively, at the sides thereof opposite the inlet openings formed in the transverse walls 117a and 118a. The fan screen 112a is carried by radially extending ribbing 32 fixed to the transverse wall 118a, and the fan screen 113a is positioned in any suitable manner at the end of the motor 30.

The fan housing 31 comprises a pair of cup-shaped members in nested relation and a sleeve or ring 33 which is formed with a portion of reduced diameter to receive an end of the cup-shaped member which forms a wall part of the suction creating chamber 11511. The fan housing 31 and rear cap 23 are disposed in end to end relation and together form a shell or enclosure, the fan housing portion 31 being disposed within the outer casing 20 and the rear cap portion 23 projecting beyond the end of the outer casing. A ring-shaped element 34 of the form shown in Fig. 10 is interposed between the abutting ends of the fan housing 31 and rear 'cap 23. The element 34 desirably is formed of a material like rubber, for example, which is resilient and also possesses electrical insulating properties.

When the rear cap 23 is removably secured to the end of the casing 20, in a manner to be described presently, the air inlet end of the fan housing 31 snugly fits against a ring 35 of insulating material, such as rubber, for example, retained in the outer peripheral edge portion of the apertured partition 28. Also, one end of the motor 30 is held in position by a ring 36 of rubber or like material retained between inwardly and outwardly extending flanges 37 and 38 provided on the sleeve 33 and motor 30, respectively. In addition,

the opposite end of the motor 30 is held in position by a ring 39 of rubber or like material retained between a flange 40 of the motor and inner face of the end wall 24 of cap 23. In view of the foregoing, it will now be understood that the enclosure formed by the fan housing 31 and rear cap 23 is resiliently held in position against the partition 28 by the ring 35, and the motor 30 and fans a and 111a fixed to the shaft 116a are resiliently held in position between the rings 36 and 39.

The rear cap 23 is removably secured to the casing 20 by a pair of elongated rods 41, one of which is shown in Fig. 10. To the extreme end portion of the casing 20, at the inside wall thereof, is fixed a ring 42 which forms a circular groove 43 to receive and hold the bent or hooked ends 44 of the rods 41. The rods 41 extend through openings in the circular element or ring 34 and extendlengthwise of the rear cap 23 in the annular space 54 formed between the latter and an outer rear hood 45 which is disposed about the cap. The rear hood 45 is formed with an inwardly extending ledge or shoulder 46 which is apertured to receive the rods 41. The threaded outer ends of the rods 41 receive tightening nuts 47, springs 48 being provided on the rods between the tightening nuts and shoulder 46 which are placed under compression when the hood is secured in 'position by the nuts 47. The rods 41 are also provided with flanges or washers 49 which are rigidly secured thereto and act against a shoulder 50 formed on the rearcap 23, whereby the latter is held snugly against the end of the sleeve 33.

It will now be understood that the detachable connection for the rear cap 23 and hood 45, which includes the springs 48, resiliently holds the inlet end of the fan housing 31 against the rubber ring 35 at the partition 28. Air discharged from the periphery of the second fan wheel 111a and flowing through the gap between the fan screen 113a and side wall of the fan housing 31 enters the motor at 51 to eifect cooling thereof. The rear.cap 23 is formed with an axially extending wall member 52 to change the direction of flow of air emerging from the motor at 53 and flowing over the latter, the air finally being discharged from the rear cap at 25, as previously explained. The axially extending wall 52 is provided in the cap 23 to eliminate noise and for this reason the rear cap usually is referred to as. a sound hood.

The ring 34 provides a seal between the rear cap 23 and sleeve 33 which also serves as a front suspension ring or region of support for the front end of the motor 30, as explained above. The ring 34, together with the ring 35, efiectively insulates the fan housing 31 and rear cap 23 from the outer casing 20. The ring 34 also includes a 'tab portion 34a which extends axially of the vacuum cleaner and serves as a guide and separator between the ring 42 at the inside of the casing 20 and the fan housing 31.

Due to the sealing effected by the ring 34, air flowing through the cleaner will not pass through the space 54 beneath the external hood 45 and rear cap 23, thus avoiding the necessity of sealing off the space 54. Also, the resilient attachment for the rear hood 45 to the body of the vacuum cleaner serves to protectthe latter when the cleaner is subjected to any sudden jarring action, as when the cleaner is placed in an upright position and supported by the end plate 26., In such event, any sudden jars will not be transmitted to the outer hood part 45.

In view of the foregoing, it will be seen that the motor-fan unit in Fig. 10 is in side-by-side relation with the space for the dust collecting receptacle 29, and that the axis of rotation of the motor-fan unit is disposed lengthwise of the casing 20 for producing flow of .air therethrough and removing dust from objects with the aid of a nozzle through which air is drawn or sucked into the receptacle 29.

The fan system of Fig. 10 and driving motor 30 therefor are embodied in the elongated casing 20 in such manner that the fan system, which embodies the principles of the invention and is generally like the fan system of Figs. 2 and 3, is of the largest possible size to produce optimum suction power. Since an increase in the size of the fan housing within certain limits will increase the suction power developed by the vacuum cleaner, it is desirable to provide an arrangement of parts like that shown in Fig. 10 and just described in which the radial gap 55 between the fan housing 31 and outer casing will be at a minimum and the fan housing will be of maximum size for a vacuum cleaner having a cross-sectional area of a given size, the sole purpose of the gap being to provide the requisite electrical insulation of the fan housing from the outer casing.

In Fig. 11 I have shown another application of my invention in which the outer casing of the vacuum cleaner also forms a part of the housing for the fan system. As in Fig. 10, an apertured partition 28]) is provided in the casing 20b at one side of which is disposed a dust bag 2912. At the opposite side or" the partition 28b is disposed a fan motor unit including rotatable fan wheels lltlb and 1111) fixed to a shaft 11612 which is driven by an electric motor 301:.

The fans 1101) and 1111) are disposed in suction creating chambers 11411 and 115b, respectively. The inlet 56 for the chamber 11 1b is formed in a transverse Wall 117b fixed to the outer peripheral edge portion of the partition 28b. The inlet 57 for the chamber 115b is formed in a transverse wall 1181: which is fixed to the inside wall of the casing by a circular member 58, the latter being formed to receive and hold a rubber ring 59 secured fast to the outer peripheral edge portion of the wall 11817. To the rubber ring 59 is also fixed one end of a member 69 of cylindrical form, the opposite end of which is held in position within the casing by a rubber ring 61. The rubber ring 61 is provided at the region the ends of casing 20b and rear hood 451) are held in abutting relation.

A fan screen 112b, which is fixed in position alongside fan Wheel 11Gb at the side thereof opposite the inletopening 56, is carried by radially extending ribbing 32b fixed to the transverse wall 118b. A fan screen 113b, which is positioned alongside the fan wheel 111k at the side thereof opposite the inlet opening 57, is supported in any suitable manner at one end of the motor 30b.

-In the embodiment being described, it will be seen that the part of the fan housing within which fan wheel 110b is disposed, is defined by the transverse walls 117b and 118b and a portion of the outer casing 20b. The part of the fan housing within which fan wheel lllb is disposed, is defined by the tranverse wall 118b and cylindrical member 60, the inlet end of which is insulated at 59 from the outer casing. As in the embodiment previously described, the gap 551) between the fan housing for fan lllb and the casing 29b is at a minimum and only sufficiently wide to insure the desired electrical insulation of the fan housing from the outer casing.

In order to provide a horizontal tank type vacuum cleaner as economically as possible, it is desirable to limit the exterior dimensions of the cleaner body. One factor in developing satisfactory suction power in a vacuum cleaner is to employ a fan system having a crosssectional area of maximum diameter. In the horizontal tank type cleaners of Figs. 10 and 11, these conflicting factors have been resolved by employing for an outer casing of a given cross-sectional area, a fan housing of maximum diameter, such fan housing being related to other parts of the fan system in accord with the invention to produce optimum suction power.

This optimum suction power capable of being developed in the horizontal tank type cleaners of Figs. 10 and 11 can best be demonstrated by reference to Fig. 6. In Fig, 6 the curves having a suflix 1b designates curves produced from test data taken from tests made with a horizontal tank type cleaner having a fan system like that shown in Fig. 1 a known type of fan system; and the curves having a suffix 2a designate curves produced from test data taken from tests made with a horizontal tank type cleaner having a fan system like that shown in Fig. 2.

The H curves in Fig. 6 are the so-called suction test curves in which the vacuum H (in millimeters of water column) is related to the quantity or volume of air q (in cubic meters per minute) sucked or drawn in per unit length of time. All of the curves in Fig. 6 are obtained from test data taken with vacuum cleaners having the same resistance to air flow, such resistance curve being indicated at In in Fig. l. The power remaining for useful cleaning purposes, after deducting the losses which occur, is the product of the vacuum produced (kg/m3, for example) and volume of air sucked per unit length of time (m. /second, for example). The ratio of the suction power to the electrical energy input to the motor, both converted to the same units which may be watts, for example, gives the data to plot the efficiency curves (1 in Fig. 6. It is to be understood that the efficiency curves 1 and 1 have been obtained from tests for fan systems like those shown in Figs. 1 and 2, respectively, which take up the same amount of space and have been operated with the same electrical energy input.

In Fig. 6 it will be noted that the suction test curve H25. for the fan system of Fig. 2 is higher than the suction test curve Hlb for the known fan system of Fig. 1. By increasing the speed at which the fan wheels of Fig. 1 are driven, it is possible to shift the suction test curve Hlb upwardly, so that the central region thereof is essentially at the same height as the central region of the suction test curve H2a. However, this would require an increase in electrical consumption of about 20%.

In Fig. 6 are also indicated the air-resistance curves for different objects. The points at which the several air-resistance curves intersect the suction test curves represent the working points to show the suction or vacuum and volume of air sucked or drawn in per time unit when cleaning different types of objects. When sucking dust on smooth surfaces, as with a brush manipulated over a Wooden floor, the dust generally is more or less in a freely accessible position and the cleaning operation primarily resides in transporting and moving the dust to the dust bag. On the other hand, carpeting must be pressed down by a nozzle manipulated over such an object which produces substantial resistance to flow of air toward the nozzle inlet.

When reference is made in Fig. 6 to the working point P: of the air-resistance curve for a wooden floor, the volume of air sucked is relatively great but the vacuum developed is equivalent to a water column of about 60 mm. When cleaning a dense cotton carpet, the vacuum developed at the working point Pclo is equivalent to a water column of about 900 mm.; and when cleaning a more porous carpet, the vacuum developed at the working point Pdc is equivalent to a water column of about 570 mm. The average value of vacuum developed for the two objects given by way of illustration, is equivalent to a water column of about 735 mm. This point on the suction test curve I'IZa is approximately at a central region of the curve, a region at which the vacuum cleaner is working with comparatively small volumes of air. However, under such cleaning conditions the increase in efficiency of the fan system of Fig. 2 over the known fan system of Fig. 1 is of substantial magnitude.

In view of the foregoing, it will be apparent that a vacuum cleaner must function aero-dynamically to meet Widely different operating conditions. In one case the function of the vacuum cleaner is primarily one of surface cleaning, as when moving a brush over a wooden floor, for example. In such event, the fan system desirably should function to effect surface cleaning which primarily involves producing a strong air stream along the floor surface which means moving a relatively great volume of air per unit length of time.

When cleaning porous objects, the air stream necessarily must flow through the object to effect loosening of dust particles lodged in the pores therein. In this case a relatively great resistance to air flow must be overcome under working conditions where the volume of air passing through the cleaner per unit length of time is comparatively small. In such event, it is exceedingly important to employ in a vacuum cleaner a fan system capable of producing a relatively high vacuum. In fan systems constructed in accord with the invention, it will be apparent from the foregoing explanation of the curves in Fig. 6 that both of the widely different cleaning conditions encountered in practice are met satisfactorily.

Although particular embodiments of the invention have been diagrammatically shown, it will be obvious that the invention may be used in many different ways without departing from the basic principles described. For example, while the fan systems compared above include two tandem fans, the improved suction capacity can be developed in a vacuum cleaner using a single fan, a pair of fans or a greater number of fans constructed in accordance with basic principles of the invention. It is therefore contemplated in the following claims to cover all such modifications and changes which come within the true spirit and scope of the invention.

What is claimed is:

1. In a horizontal tank type vacuum cleaner, an elongated casing providing a space lengthwise thereof adapted to receive and hold a dust collecting receptacle, a motorfan unit within said casing in side-by-side relation with the space for the receptacle and having the axis of rotation thereof disposed lengthwise of said casing for producing flow of air therethrough and removing dust from objects with the aid of a nozzle through which air is drawn or sucked into the receptacle, said motor-fan unit including an electric motor and fan structure comprising a centrifugal fan having a rotatable fan wheel formed with an inlet at one side thereof at the vicinity of its axis of rotation and an outlet at the outer periphery thereof, a fan screen transverse to said axis having one side thereof spaced from and facing the side of said fan wheel which is opposite said inlet, means providing a housing for said fan wheel and fan screen which is formed with an inlet cooperating with said fan wheel inlet, said fan housing being of maximum diameter for said casing and having a cross-sectional area essentially the same or approaching the cross-sectional area of said casing, the diameter of said fan screen being greater than that of said fan wheel so asto throttle the annular air passage at a region at the immediate vicinity of said fan wheel,

outlet from which air is discharged into such throttled region, and the ratio of the product of the diameter of said fan housing and outer diameter of said fan screen to the product of the diameters of the fan housing inlet and fan wheel inlet being in a range which is between and including eleven and nineteen to operate said cleaner at or substantially at optimum efficiency and at a relatively high vacuum, for a definite rate of power consumption by said motor and given speed at which said motor is driven, when the nozzle must be pressed against a porous object like a carpet, for example, to create substantial resistance to air flow and cause a comparatively small air flow through said casing.

2. In a horizontal tank type vacuum cleaner, an elongated casing, means in said casing for separating dust from air flowing therethrough, a motor-fan unit within said casing in side-by-side relation with said dust separating means and having the axis of rotation thereof disposed lengthwise of said casing for producing flow of air therethrough, said motor-fan unit including an electric motor and fan structure comprising a centrifugal fan having a rotatable fan wheel formed with an inlet at one side thereof at the vicinity of its axis of rotation and an outlet at the outer periphery thereof, a fan screen transverse to said axis having one side thereof spaced from and facing the side of said fan wheel which is opposite said inlet, means providing a housing for said fan wheel and fan screen which is formed with an inlet cooperating with said fan wheel inlet, said fan housing being of maximum diameter for said casing and having a cross-sectional area essentially the same or approaching the cross-sectional area of said casing, the diameter of said fan screen being greater than that of said fan wheel so as to throttle the annular air passage at a region at the immediate vicinity of said fan wheel outlet from which air is discharged into such throttled region, and the ratio of the product of the diameter of said fan housing and outer diameter of said fan screen to the product of the diameters of the fan housing inlet and fan wheel inlet being in a range which is between and including eleven and nineteen to develop substantially optimum suction power with comparatively small quantities of air flow for cleaning purposes and the like at a definite rate of power consumption by said motor and given speed at which said motor is driven.

3. A horizontal tank type vacuum cleaner as set forth in claim 2 in which said ratio is at or in the vicinity of fifteen.

4. A horizontal tank type vacuum cleaner as set forth in claim 2 in which said means providing the housing for said fan wheel and fan screen includes said casing.

5. A horizontal tank type vacuum cleaner as set forth in claim 2 in which said means providing the housing for said fan wheel and fan screen comprises a shell having a cross-sectional area approaching the cross-sectional area of said casing, said shell being electrically insulated from said casing to provide a gap therebetween which is at a minimum and yet will provide the requisite insulation of said shell from said casing.

6. A horizontal tank type vacuum cleaner as set forth in claim 2 in which said means providing the housing for said fan wheel and fan screen comprises a shell having a cross-sectional area approaching the cross-sectional area of said casing, means for mounting said fan structure "and motor as a unit in said casing, said mounting means including provisions for utilizing the space within said casing substantially entirely as a fan housing space.

References Cited in the file of this patent UNITED STATES PATENTS 993,985 Hacher May 30, 1911 2,149,135 Erikssen-Jons Feb. 28, 1939 2,285,338 Kidney June 2, 1942 2,322,948 Lofgren June 29, 1943 2,450,671 Loss Oct. 5, 1948 

